This invention relates to aluminum containers. More particularly, this invention relates to an aluminum container having an inner surface treated to suppress foaming of carbonated liquids subsequently placed therein.
Aluminum containers used in the food and beverage industry are normally coated with organic lacquers or paints, i.e. organic coating materials capable of curing to form an adherent continuous film on the surface. To obtain proper adherence of such organic materials to the aluminum, it is customary to first clean the surface of the aluminum and then to apply an inorganic coating material known in the trade as a conversion coating. This involves treating the surface with a solution containing ions of phosphate, hexavalent chromium, and fluoride. The organic coating is then applied thereon.
It has been found that this conversion coating actually provides, from a biological standpoint, a satisfactory coating without the need for further application of organic coating materials. This, of course, results in considerable savings. However, when a container having only such a conversion coating on its surface is subsequently filled with a carbonated liquid such as beer or the like, the liquid has been found to excessively foam, thus interfering with the filling operation and reducing the carbonation and resultant foamability of the liquid when later poured into a glass or the like.
Quite surprisingly, I have discovered that an aluminum container which has been treated to form a conversion coating theron can be further treated to suppress subsequent foaming of carbonated liquids therein.